The invention is based on a fuel injection pump as generally defined hereinafter. In a known fuel injection pump of this type (German Offenlegungsschrift 24 46 903), the supply onset of the injection pump is determined by the plunging of the oblique groove into the control slide, after which the conduit leading to the pump work chamber is blocked, so that the injection pressure can build up therein. The end of supply and thus the injection quantity is determined by the rotational position of the control slide, according to which the required stroke of the pump piston between the supply onset and the opening of the discharge bore is variable by the oblique groove. Viewed in terms of the drive shaft (camshaft), the supply onset (injection onset) is varied by the axial displacement of the control slide, and the injection quantity itself is determined by the rotation of the control slide.
Because of the obliquity of the oblique groove, its blockage to effect the supply onset is not effected with an abrupt closure, as desired; instead, there is a gentler transition, on the order of a pre-stroke control. In cooperation with the control of the end of supply, this makes exact metering difficult, because the throttle effect resulting in this type of control is variable in accordance with rpm. While a relatively large amount of fuel can still flow out at low rpm, less fuel is diverted at high rpm, because of the increased throttling effect that results. Since this effect seldom corresponds to the desired course of the fuel quantity, it must be corrected once again by a regulating apparatus. Because the filling of the pump work chamber also takes place via the oblique groove in the vicinity of bottom dead center of the pump piston, the conduit extending in the pump piston must be extended far downward, in order to attain sufficient filling, but this means that there is a relatively large idle volume. With this type of fuel quantity control problems arise when the engine is shut off, that is, not the least of which is a zero supply quantity. To this end, the control slide is rotated such that the diversion bore opens the oblique groove before the lower end of this groove plunges into the control slide. At higher rpm, the resultant throttling effect produces a residual injection quantity, instead of the immediate interruption of injection that is desired. Pumps of this kind, controlled by a control slide, are primarily used for very large engines, in which this undesirable injection is particularly disadvantageous, sometimes even dangerous, because these motors, after the fuel is shut off, are substantially stopped by means of their inherent compression.